Hydrodesulfurization process



July 10 1951 P. w. CORNELL HYDRODESULFURIZATION PROCESS Filed Dec. 14, 1948 Ea l NEU OQ @0d ATTORNEV Patented July 10, 1951 HYDRODESULFURIZATION PROCESS Paul W. Cornell, Mount Lebanon, Pa., assignor to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Application December 14, 1948, Serial No. 65,153

4 Claims.

This invention relates to a method for repressurizing a contact hydrodesulfurization process and more particularly to a method of repressurizing a hydrodesulfurization system after the contact agent has been regenerated by the use of readily liquefable low boiling hydrocarbon gas.

The contact or adsorption hydrodesulfurization process has furnished the rener of crude petroleum with one of the most eiiicient methods of removing sulfur from sulfur-bearing charge stocks. As described in U. S. applications Ser. Nos. 699,671 and 699,672 led September 27, 1946, by W. A. Horne and J. F. Junge (now Patents 2,516,876 and 2,516,877, respectively), this process consists in contacting a petroleum hydrocarbon and hydrogen-containing gas mixture in the presence of a contact agent comprising an iron group metal oxide such as nickel oxide on a carrier at an elevated temperature and pressure. The process is continued until substantial amounts of hydrogen sulde appear in the eilluent at which time the process is stopped and the contact agent regenerated to substantially its original form. Following the regeneration the system is represssured and once again put onstream and the process continued as before.

It had been found that on repressurizing the system with a hydrogen-containing gas, such as a mixture of hydrogen and hydrocarbon charge the hydrogen initially reacts with the iron group this partial removal of hydrogen, the pressure in` the system falls causing undesirable iiuctuations in pressure. The practical result of this has been the requirement of an enlargement of the hydrogen producing and compressing equipment and/or anincrease in the facilities for storing excess amounts of hydrogen. Consequently, a large expenditure is necessitated for additional hydrogen apparatus to meet the relatively short repressuring and initial on-stream periods when the consumption of hydrogen is greatly in excess of average.

An object of the present invention is to provide a method whereby contact hydrodesulfurization systems may be repressurized after regeneration without substantial pressure fluctuation or undue hydrogen consumption.

A further object of the present invention is to provide a method whereby contact hydrodesulfurization systems may, bevput ori-streamlaiter 2 regeneration without initial undue hydrogen consumption. e

A still further object of the present invention is to provide a method whereby contact hydrodesulfurization processes are repressurized without excessive pressure drops.

Another object of the present invention is to provide a method whereby contact hydrodesulfurization processes are put on-stream without excessive falling of the pressure of the system.

Further objects will appear hereafter.

These and other objects are achieved by the present invention which comprises an improvement for a contact absorption hydrodesulfurization process in which high boiling vaporous petroleum hydrocarbons containing sulfur, and hydrogen-containing gases under pressure, are passed together through a chamber containing a contact agent comprising substantially an iron group metal oxide on a carrier, which contact agent absorbs `the sulfur content of the petroleum hydrocarbons with a concomitant conversion of the iron group metal oxide into iron group metal sulde, following which the contact agent is regenerated to susbtantially its original form and the contact absorption hydrocarbon process renewed; the said improvement comprising avoiding pressure drops and surges when the contact absorption hydrodesulfurization process is renewed by bringing the system to substantially the operating pressure after the contact agent has been regenerated by introducing a readily liquei'lable low boiling saturated hydrocarbon gas into the chamber and when substantially the desired pressure has been attained, again contacting the petroleum hydrocarbons and hydrogen-containing gas with the iron group metal oxide in the pressured-up chamber.

The present application is similar to the aforementioned Horne and Junge applications as regards the operating conditions and type contact. The present application is an advance over the above applications in that I have discovered that by repressurizing the system following regeneration by the use of readily liqueable low boiling hydrocarbon gas instead of hydrogen-containing gas the pressure drop heretofore encountered can be avoided. Also, if readily liquefiable low boiling hydrocarbon gas is used in conjunction with hydrogen-containing gas and petroleum hydrocarbon vapor at the commencement of the on-stream cycle, the initial on-stream pressure drop due to hydrogen consumption can likewise be avoided.

The reaction takes place at varying temperatures, pressures and .spacevelocities .with the optimum conditions depending on the type charge stock that is used. For example, with low boiling hydrocarbons such as those normally liquid petroleum fractions having as ASTM end point below 600 F., such as straight run or cracked gasolines and naphtha, the temperature will usuall7 lie between kv600 .and 80.0 F. I havefollnd that at temperatures "below .600 F., the desulfurization activity of the contact diminishes whereas with temperatures higher than 800 F. excessive cracking reactions result in decreased product recovery and rapid coke formation which deactivates the contact. I have further found that the optimum pressures lie between 1f00 :and 500 p. s. i. g. At pressures below 100 p. s. i. g. the partial pressure of hydrogen is not sufficient to maintain desulfurization activity `nor 4to suppress cracking reactions which result in coke formation. Increasing the pressure above 500 p. s.'i. g. results in only a slight incremental gain in desulfurization, and a decrease in-the bromine num- ;berf the end product gasoline and is thus not commercially desirable. The preferred space velocitiesflie Ibetween'1;0 and 6.0 liquid volumes of charge per hour per volume of contact agent. ASpace velocities below 1.0 Yresult in excessive cracking and olefin saturation reactions caused ,by the long contact `time whereas at space velocities above'6.0 'the contact time is too short to provide sufficient desulfurization.

YThis invention can be applied with exceptional success to high boiling petroleum Yhydrocarbon oil such as total ,crude as well as Vtopped or reduced crude. These terms may he deled as follows: T otalgcrude is dened as naturally occurring )Jlroleum Voil which 'has not been processed in any `manner but has been or `preferably should be .separated from water or sediment and desalted. Topped or reduced crude is defined as the residual ,petroleum oil resulting fromremoval of all or someof the straight run fractions such ,asl`gas, gasoline, kerosene, naphtha, furnace oil, gas oiletc.`which are normally removed from the ,above-defined total crude ,by the process of atmospheric and/or vacuum topping or distillation. Charge stocks such as total crude ,whichghas been diluted or admixed with 'lower boiling straight run or cracked Ypetroleum fractions including 5gases are also included. Diluents of this kind mayjbe required in processing low gravity crudes suchassome of those from Mississippi as well as those from'Kuwait. 'Diluents may -also be neces- ,sary and `preferred*indesulfurizing topped Yor reduced ,crudes The purpose of this diluent is to assist vaporization of the heavier Aconstituents of the charge stock. In some cases it may be desirable-to admix steam with/the charge stock to assist vaporization. Preferred operating conditions for ,the aforementioned high boiling petroleum hydrocarbons-mayvary within certain ranges depending upon the charge stock.

`Lhave found the optimum temperature range to` be from 750 to 950 F. for high boiling petroleum hydrocarbons. YAt temperatures below '-'750,'F. the desulfurizing'activity of the contact diminishes whereas attemperatures greater than '950F. excessive cracking actions result in `decreasedgproduct recovery and rapid coke formation which deactivates the contact. I have further ascertained `the preferred pressure range to b ebetween 100 and 1000 p. s. i. g. With pressures below 100 Yp. -s. i. g. it appears that the partial pressure of hydrogen is not sufficient to maintain .desulfurizing activity norto suppress cracking reactions-whichresult in coke 'formal,locity ,below Ytheformer causes excessive crack- -ing vreactions due to the long contact time, while space velocities above 6.0 are too short to allow .sufficient desulfurization. I have found that best results are obtained with a hydrogen ratio to petroleum hydrocarbon greater than 300 s. c. f./bbl.

vAs disclosed in the aforementioned Horne and Junge applications, the contact comprises a substantial amount of an iron group oxide i. e. `nickel,iron or cobalt oxides supported on a carriersuch as alumina. Other carriers which have been found to be applicable include kieselguhr, silica gel, aluminum silicates, silica-aluminas, Alf-ra-x, Magnesol, VPoroceL bauxite, diatomaceous earth, etc. The contact agent may be prepared by any Aof the known methods such as single or multiple impregnation, coprecipitation, adsorption from a colloidal solution, etc.

The present process is best understood by an examination of the accompanying figure. Crude charge enters the system through line I0 and vpasses by means of charge pump I2, through line I3,-and line I4into heat exchangers I6, I8 and 20. The charge then passes by means of line 22 into oil and hydrogen heater 24,

The hydrogen is prepared from fuel gas which enters the system lfrom line Y26 through line 28 into khydrogen producing plant 30. `The hydrogen may most advantageously be produced by means of the conventional reforming and shift reactions, in which the'fuel gas is Iburned in the presence of steam, and the carbon monoxide formed in the reaction is converted to carbon dioxide. The hydrogen Vplus carbon dioxide produced in plant 30 is passed by means of line 32 into gas holder '34 where it may be stored before being -returned to plant 30 by-passing it through line '35, raw hydrogen compressor 36, and line 31. In hydrogen vproducing plant 30, the carbon dioxide is removed Yby conventional means, and the puried and compressed hydrogen is then removed --from hydrogen Aproducing plant 30 by means of line 38, and lpasses through compressor pump 40 -to line I4 where it joins the crude petroleum vcharge coming from line I3. The hydrogen plus charge likewise passes from line I4 through heat exchangers I6, I8 and 20 into line 22 and then into oil and hydrogen heater 24. In oil and hy drogen -heater24 the charge and hydrogen are heated to reaction temperature and then passed by means of line 42, valve 44 and line 4S into reactor 48. Alternatively, valve 44 may be closed and the oil and hydrogen mixture passed from heater 24 through line 42 into line 50, valve 52, line 54 and thence into reactor 50. By alternat ing, one reactor may always be kept on-stream while the other is being purged, or regenerated. 'While only two reactors are shown, a greater numbermay be provided so that one or more may be in the processing stage, while the remaining reactors are at'other stages in the reaction cycle. In the-reactors the petroleum hydrocarbons are hydrodesulfurized `by passing over the contact agent comprising substantial amounts of an irongroup metal oxide on a carrier, thereby causing the sulfurto be removed from the charge stock by combination as sulfide with the contact agent `kept nffthe Vreactors. The -desulfurized product is passed from reactor 48 into line 58, valve 60 and into line 62. If reactor 56 is on stream desulfurized product from reactor 56 is passed by means of line 64, valve 66, and line 68 into line 62. The desulfurized product in line 62 is passed in heat exchanger relationship through heat. exchanger 20, and line 64, where a portion is diverted through heat exchanger 66 and line 68 While the remainder is passed through heat .exchanger I8. The product from heat exchangers I8 and 66 are then passed in heat exchanger relationship through heat exchanger 6 into line 10, lcondenser 12, line 14 into high pressure flash drum' 16.

In high pressure ash drum 16 the 'recycle gas is separated from the desulfurized liquid product. The recycle gas passes through line 18 Where it is apportioned. Part of the gas from line 1 8 passes into line 80 and then into recycle hydrogen compressor 82 and line 84 from which it joins the charge stock hydrogen mixture in line I4. The 'remaining portion of the recycle gas is passed from line 18 into line 86, line 90 and line 28 where it joins the fuel gas entering the system from line 26. From line 28 the fuel recycle gas mixture is passed to hydrogen producing plant 30 for hydrogen manufacture.

The desulfurized liquid product from high pressure flash drum 16 is passed through line 92- into low pressure flash drum 94. Any water present in high pressure ash drum 16 is removed from the system by means of Water separator 96 and pipe 98. In low pressure ash drum 94 the liquid product is removed by means of line and transfer pump |02 to line |04. From Aline |04 the product is removed from the system ents such as methane and ethylene from low Apressure flash drum 94 are removed as overhead from reboiled absorber ||2, passed into line |20 and thence into line 90, line 28 into hydrogen producing plant 30. In reboiled absorber ||2 the normally liqueable hydrocarbons as well as lthose liqueable under pressure such as the three-carbon' hydrocarbons vand above are removed together with the lean oil in which they are dissolved as bottoms by means of line |22,

heat exchanger |24, line |26, ypassing therefrom into stripperV |28.

The `distilling conditions in stripper |28 are maintained by means of line |30, heat exchanger 66 and line |32. The lean oil bottoms from stripper |28 are removed by means of line |34, pass in heat exchanger relationship through heat exchanger |24, line |36, lean oil pump |38,`line 40, cooler |42, line |44 into reboiled absorber ||2 Yfor use as absorption oil. The overhead .vapors from stripper |28 are discharged through line |46, condensed in condenser |48 and then passed through line |50, reflux drum |52, line |54 into stripper reflux pump |56 where a portion of the overhead is returned as reiiuxv to stripper |28 by means of line |58 The remainder Vof the overhead from stripper |28 is removed through line |60 and passed to depropanizer |62.

, The distillation conditions in depropanizer |62 are maintainedby means of line |63. vaporiz'er 6 li |65 and line |61. The bottoms 'from the depropanizer |62 comprising desulfurized product'. areremoved by means of line |64 and passed to line |06 where they join the desulfurized prod'-A uct from low pressure flash drum 94 and are removed from the system. The overhead from depropanizer |62 comprising liquefiable hydro' carbon gases such as propane is removed by line. |66 and condensed in condenser |68. The condensate is then passed through line |10, reflux drum |12, line |14v into pump |16. YFrom pump |16 the overhead condensate from depropanizer' |62 passes into line |18 where a portion of it; is returned as reux to depropanizer |62 by means of line |80. The remainder of the de propanizer overhead condensate in line |18 is.

passed by means of line |82 to propane storager drum |84 where it is stored inthe liquidl state..

At the completion of the on-stream cycle, which may be determined by the appearance or". substantial amounts of hydrogen sulde in ther eluent, regeneration of the contact agent be comes necessary. In some instances it may ber feasible to commence regeneration at another time this to be determined by the content of the carbon residue of the product. The onstream cycle is stopped by closing valves 44 or The contact beds are then regenerated by first purging the reactors with an inert substance such as steam. The purpose of the purge is to recover valuable hydrocarbons which remain in the contact bed. The inert substance is introduced into reactor 48 by means of lines 45 and 46 and may leave the reactor through line 58, valve 60 and line 62, or through line 58 and a valve, condenser,` and lines (not shown) to drum 94. The inert substance for reactor 56 is introduced by means of lines 53 and 54 and leaves the reactor by means of line 64, valve 66, line 68 and line 62, or through line 64,`and a valve, condenser and lines (not shown) to drum 94. Following the purge, valves 69 or 66 are closed andv regenerating gas such as oxygen or an oxygen-containing cas such as air is introduced into reactors 48 or 56 from lines 45 and 46, Vor 53 and 54 by opening valves 41 or 55. In reactor 48 or 56 the contact bed is oxidized and the vsulfur on the contact surface is removed as sulfur dioxide. This regeneration product gas is removed from reactors 48 or 56 by their corresponding lines 51 and 63, and valves 59 and 65. The sulfur dioxide in this gas may be recovered in conventional manner such as by solvent absorption and stripping. The sulfur difoxide free regeneration off-gas may then serve to dilute the first regeneration gas admitted to the reactors. Alternatively, the sulfide dioxide gas containing regeneration off-gas may serve to dilute the fresh regeneration gas. After regeneration is complete, which may readily be determined by the fact that the contact agent is substantially free of sulfur and is once again in the oxide form, the oxidizing gas is shut off and the reactor steamed to remove any oxygen present. The reactor is then blocked off by closing valves 41 or 55. Also, valves 59 or 65 are likewise closed.

At this point reactor 48 or 56 is brought to vabout on-stream pressure by the use of applicants invention (in the accompanying drawing applicants invention appears in heavy line). Liquid propane is released from propane storage 4drum |84 by opening valves |86 and |88 and passing the liquid propane through line |90, pump |92, line |94 intovaporizer I 96.Inva

aswell@ 7 fporzer 96 ftheliqid propaneissgasified and ln'the'gaseous" form is :conducted to reactors ,-48 "or55iby :means of line` |98 and respective Avalves lkand. "When Ythefsystein hasbeen Abrought iup to Ihe'desired pressure, which-will usually approximate on-stream pressure, valve |88 vori-|36 is closed and valves `44`orf52 and'lil or 66fare opened and `flow isrestablished through' the reactor `after 'whichifthe other reactor'may be blockedl off for 'ilushing and regeneration. Furthermore, valve 'ZUUis likewise opened. Asa-consequence, a Amix- "ture .o'f "charge stock, hydrogen-containing gas andreg'ulate'd amounts of propaneiare introduced "into 'the"system. The npropane joins thecharge "stock and 'hydrogen in line 14 after passing through 'valve 2li()` and'line 202. I have found "that introducingregulated amounts of propane latthe commencement/'fof the on-stream cycle, when the "hydrogen 'consumption would other- -wis`e`be h'igherthan averageyas'lwell as prior to f'p'lacingi thereactoron-stream, further minimizes the surges 'resulting from the `Aabnormal demand for'hydrogen. After the system Yhasfbeen onst'ream for sometimegvalve 200 is closed and the purity of` th`e^charge fstock-hydrogen stream -is maintained as before.

` The above illustration'hasbeen'given with-the readilyiiqueiiable 'low' boiling `-hydorcarbon gas being'propa'ne 'Howeven vit-is to be understood that any :readily liqu'e'able hydrocarbon gas canfbe used. "It iis preferred to employ a ,gas 'formed'in' the reaction. 'The propane cut discussedin`the"ai`orementioned description is substantially propane Ebut `may .containsuch `materials as butane and ethane: and minor amounts 'of fmethan'e. In^ place of propane abutanek cut :containing"substantially butane` or mixtures of a butane andpropanecut may-be employed. However, since viorthe vproduction of gasoline, maximum butane retention in'thecrudefis desirable, and 'since for' minimizing losses inthestorage vf'the treatedcrude product,V maximum propane removalis desirable, depropanizing facilities may be a'customary part of the unit-and the liquid "overhead product from such depropanizersare- 'ierred to herein'as"propane wouldbe-available fand'hencebe" 'the preferred `materiall for use.

Although itf'is'to vbe understood=that the pracv`tice outline'din 'the' aforementioned illustration will usually "furnish`thebest'results and is to be 'considered' the preferredv procedure, the inven- "tion-may beinodiiied in certain cases by limiting "the use vofthe liqueable low boilingv hydrocarbon gas `solely to the repressurizing ofthe re- -ac'ton In the`se`cases thestep-of diluting .the `recycle charge stock-hydrogen-'containing .gas fm'ix'ture" with liqueable low boiling hydrocarbons isomitted. Alternatively, in rare casesvit 1In'ay Vbe 'desirable to repressurize the l system Awith :one substance, and to dilute the lcharge stock, `and hydrogen-containing gas mixture -with lanother. Thesevariations as well as other obvious-'modifications in` apparatusl or process lreadilyapparent to one `skilled inthe art-are to be "considered withinthe scope of my invention.

' This Vinvention permits the repressurizing of hydrodesulfurizing systems in an economicaland advantageous manner andavoidsdisturbance of `the"'temperature andpressure balances due to 'i'nitial hydrogen consumption encountered Vin lprior systems. Furthermore, the expensive-enl'largement of hydorgen-producing, compression -aiid storage facilities is replaced by the relative- .'ly inexpensive-use of the liqueable hydrocarboni system shown Y. in '.applicants specification.

This faiords a :majorveconomy in boththe. initial costand in ,the operating expense of the. convtact hydrodesulfurizationprocess inasmuch as it is .cheaper and, facile to store and handle a liqueable Ysubstancesuch as a liquefiable hydrocarbon than a .highly explosive .dangerous gas like hydrogen under .high pressure.

In addition, due to the virtual elimination of pressure surges there willbe a lengthening of the .useful life of thecontactasa result of the diminution of the stresses and strains concomitant 'with the pressuresurges. YLikewise as a result of this invention there .will be a .prolongation Yof the life of the mechanical equipment ,involved inthe process, due to -the elimination of.sudden severe surges.

What I claim is:

1. In acontact..absorpti0n hydrodesulfurizationvprocess in which a vaporous high boiling ypetroleum .hydrocarbon containing sulfur, and hydrogen-containing gas under pressure are passed together through a chamber containing la contact agent comprisingsubstantially.an iron .group metaloxide on a carrier, whichcontact agent-absorbs the sulfur contentof the petroleum hydrocarbon vwith .a Yconcomitant conversion of the iron group metal oxide into ironvgroup metal sulfide, following which the contact agent isre- .generated .to substantially its original form and the contact labsorption hydrodesulfurization .process vrenewed, -the improvement for. avoiding .pressure dropsand surges when the contact abfsorption hydrodesulfurization.process is renewed '-due-toabsorption of. hydrogen by the iron group metal oxide .and -for .obtaining more prolonged contact betweenthe.hydrocarbon and the iron group metal oxide which comprisesbringing the 'system' to substantially .the operating pressure after ythe` contact ,agenthas ,been regenerated by 40 :introducing areadilyliquefiable low boiling saturatedhydrocarbongas into the chamber containingthe regenerated contact comprising sub- .stantiailythe .irongroupsmetal oxide, and when substantially therdesiredpressure has been at- A `tained, again contacting the petroleumhydrocarbon and hydrogen-containing gas with the iron group metal-oxide inthe pressured-up chamber.

V2. In a contact absorption hydrodesulfurization processin-whicn a kvaporous .highvboiling petroleum -hydrocarbon vcontaining sulfur, and hydrof gen-containing gas .under-pressure are passed tolgether throughachamber containing a contact -agent comprisingA substantially an iron group -metal oxide on acarrier, which contact. agent absorbs the sulfur content of the petroleum hydrocarbonwith a concomitant-conversion of the iron group metal oxide into iron group metal suliide, following 4whichthev contact agent Ais' regeneratedto substantiallyfits original formand the 50 contactabsorption hydrodesulfurization 4process renewed,.the.improvement for avoiding pressure ydropsandf-surges when the contact absorption .fhydrodesulfurization process is. renewed due to Y.absorption oiftheM hydrogen by the iron groi1p fmetaloxide `and for obtaining more prolonged .contact betweenthe hydrocarbon and rthe iron group metal: oxide v4which .comprises bringing the .system to substantially the, operating ,pressure -after-.the contact agent has been regeneratedby introducing a readilyy liqueablelow boiling saturatedhydrocarbongas into the chamber containing the regenerated contact comprising substantially` iron group metal oxide, thenwhen sub- "stantially the desired` pressure has. been attained, '15 bringing the system on-stream by-.introducing'the vapors of the high boiling petroleum hydrocarbon and hydrogen-containing gas into the chamber, and maintaining a partial pressure of the readily liquefiable low boiling saturated hydrocarbon gas in the system during an appreciable portion of the initial stage of the on-stream period.

3. In a Contact absorption hydrodesulfurization process in which a vaporous high boiling petroleum hydrocarbon containing sulfur, and hydrogen-containing gas under pressure are passed together through a chamber containing a contact agent comprising substantially an iron group metal oxide on a carrier, which contact agent absorbs the sulfur content of the petroleum hydrocarbon with a concomitant conversion of the iron group metal oxide into iron group metal suliide. following which the contact agent is regenerated to substantially its original form and the contact absorption hydrodesulfurization process renewed, the improvement for avoiding pressure drops and surges when the contact absorption hydrodesulfurization process is renewed due to absorption of the hydrogen by the iron group metal oxide and for obtaining more prolonged contact between the hydrocarbon and the iron group metal oxide which comprises bringing the system to substantially the operating pressure after the contact agent has been regenerated by introducing a readily liquefiable low boiling hydrocarbon gas selected from the groupl consisting of gases containing substantial amounts of propane, gases containing substantial amounts of butane, and gases containing mixtures of propane and butane into the chamber containing the regenerated contact comprising substantially iron group metal oxide, then when substantially the desired pressure has been attained, bringing the system on-stream by introducing the vapors of the high boiling petroleum hydrocarbon and hydrogen-containing gas into the chamber, and maintaining a partial pressure of said readily liqueable low boiling hydrocarbon gas in the system during an appreciable portion of the initial stage of the on-stream period.

4. In a Contact absorption hydrodesulfurization process whereby a vaporous high boiling petroleum hydrocarbon containing sulfur, and hydrogen-containing gas under a pressure of between mmm.. 1 0 l about and 1000 p. s. i. are passed together at a temperature in the range betwen about 750 to 950 F. through a chamber containing a contact agent comprising substantially nickel oxide on a carrier which contact agent absorbs the sulfur content of the petroleum hydrocarbon with a concomitant conversion of the nickel oxide into nickel sulde, following which the contact agent is regenerated to substantially nickel oxide and the contact absorption hydrodesulfurization process renewed, the improvement for avoiding pressure drops and surges when the contact absorption hydrodesulfurization process is renewed due to absorption of the hydrogen by the nickel oxide and for obtaining more prolonged contact between the hydrocarbon and the iron group metal oxide, which comprises bringing the system to substantially the operating pressure after the Contact agent has been regenerated by introducing a readily liqueable low boiling hydrocarbon gas selected from the group consisting essentially of gases containing substantial amounts of propane, gases containing substantial amounts of butane and gases containing mixtures of propane and butane into the chamber containing the regeneratedvcontact comprising substantially nickel oxides and when substantially the desired pressure has been attained, again introducing the vapors of the petroleum hydrocarbon and hydrogen-containing gas into the chamber and maintaining a partial pressure of said low boiling hydrocarbon gas in the system during an appreciable portion of the initial stage of the onstream period.

PAUL W. CORNELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,944,236 Haslam Jan. 23, 1934 2,273,298 Szayna Feb. 17, 1942 2,287,672 Fahnestock June 23, 1942 2,337,358 Szayna Dec. 21, 1943 2,398,175 C'ole Apr. 6, 1946 

1. IN A CONTACT ABSORPTION HYDRODESULFURIZATION PROCESS IN WHICH A VAPOROUS HIGH BOILING PETROLEUM HYDROCABRON CONTAINING SULFUR, AND HYDROGEN-CONTAINING GAS UNDER PRESSURE ARE PASSED TOGETHER THROUGH A CHAMBER CONTAINING A CONTACT AGENT COMPRISING SUBSTANTIALLY AN IRON GROUP METAL OXIDE ON A CARRIER, WHICH CONTACT AGENT ABSORBS THE SULFUR CONTENT OF THE PETROLEUM HYDROCARBON WITH A CONCOMITANT CONVERSION OF THE IRON GROUP METAL OXIDE INTO IRON GROUP METAL SULFIDE, FOLLOWING WHICH THE CONTACT AGENT IS REGENERATED TO SUBSTANTIALLY ITS ORIGINAL FORM AND THE CONTACT ABSORPTION HYDRODESULFURIZATION PROCESS RENEWED, THE IMPROVEMENT FOR AVOIDING PRESSURE DROPS AND SURGES WHEN THE CONTACT ABSORPTION HYDRODESULFURIZATION PROCESS IS RENEWED DUE TO ABSORPTION OF HYDROGEN BY THE IRON GROUP METAL OXIDE AND FOR OBTAINING MORE PROLONGED CONTACT BETWEEN THE HYDROCARBON AND THE IRON GROUP METAL OXIDE WHICH COMPRISES BRINGING THE SYSTEM TO SUBSTANTIALLY THE OPERATING PRESSURE AFTER THE CONTACT AGENT HAS BEEN REGENERATED BY INTRODUCING A READILY LIQUEFIABLE LOW BOILING SATURATED HYDROCARBON GAS INTO THE CHAMBER CONTAINING THE REGENERATED CONTACT COMPRISING SUBSTANTIALLY THE IRON GROUP METAL OXIDE, AND WHEN SUBSTANTIALLY THE DESIRED PRESSURE HAS BEEN ATTAINED, AGAIN CONTACTING THE PETROLEUM HYDROCARBON AND HYDROGEN-CONTAINING GAS WITH THE IRON GROUP METAL OXIDE IN THE PRESSURED-UP CHAMBER. 